Insight: crops will face more extreme heat during flowering season
by Sharon Gourdji, environmentalresearchweb, August 26, 2013
Extreme heat during the flowering period of crops
can interfere with pollination and grain formation, and severely reduce
yields. Along with increases in global mean temperature, extreme heat
events – where temperatures cross crop-specific critical thresholds –
are becoming increasingly common. In this study,
we found that wheat around the world has been exposed to extreme heat
in the last 30 years and project that wheat, maize and rice will be
exposed to three times as much heat by the 2050s.
We started with global maps of harvested areas for four major crops:
maize, rice, soybean and wheat. We then paired these regions with crop
calendars and air temperatures between sowing and harvest for each year
from 1980 to 2059. As well as calculating growing season mean
temperatures, we identified a 30-day window around flowering in the
middle of the season, and then counted the number of days in this period
when temperatures crossed critical values, and where we would expect to
see large yield declines. These temperatures are 34˚C for wheat, 35˚C
for maize, 36˚C for rice, and 39˚C for soybean.
We then constructed historical air temperatures from 1980 to 2011 by interpolating weather station data. Future temperature projections up to the 2050s were taken from a range of climate models included in the CMIP5 inter-comparison project.
Our results show that maize has the highest current exposure to heat,
with 15% of the total global area being exposed to temperatures above
the critical temperature in the 2000s. Wheat in the Middle East and
Central and South Asia has become increasingly problematic in recent
decades, while the main rice-growing regions in South, East and
Southeast Asia are expected to cross temperature thresholds increasingly
in the next 30 to 40 years.
While faster plant growth at higher temperatures may lead to earlier flowering and somewhat reduced extreme heat exposure for wheat grown in temperate areas, this will have little impact for crops grown in tropical locations, where the temperature varies little throughout the year. Other environmental change factors, such as rising atmospheric carbon dioxide and changes in soil moisture, will also affect crop yields in coming decades. That said, stress during the reproductive period will continue to present a risk for crop production regardless of other beneficial changes. Farmers, working with all levels of government, need to think proactively about how to prepare for these changes through crop and variety switching, shifting sowing dates, irrigation and agronomic management, and potentially moving cropping systems to other regions altogether.
We then constructed historical air temperatures from 1980 to 2011 by interpolating weather station data. Future temperature projections up to the 2050s were taken from a range of climate models included in the CMIP5 inter-comparison project.
While faster plant growth at higher temperatures may lead to earlier flowering and somewhat reduced extreme heat exposure for wheat grown in temperate areas, this will have little impact for crops grown in tropical locations, where the temperature varies little throughout the year. Other environmental change factors, such as rising atmospheric carbon dioxide and changes in soil moisture, will also affect crop yields in coming decades. That said, stress during the reproductive period will continue to present a risk for crop production regardless of other beneficial changes. Farmers, working with all levels of government, need to think proactively about how to prepare for these changes through crop and variety switching, shifting sowing dates, irrigation and agronomic management, and potentially moving cropping systems to other regions altogether.
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